A generally-used light-emitting module includes a housing in which a light-emitting device (LD: laser diode or LED: light-emitting diode) and an optical fiber are provided so that a light-emitting end surface of the light-emitting device and one end (hereinafter, referred to as a “light-receiving end”) of the optical fiber face each other. Further, the other end (hereinafter, referred to as a “light-emitting end”) of the optical fiber is drawn out from a neck portion of the housing and extends to the outside of the housing. A light-emitting module including an LD as the light-emitting device is called an LD module or the like, whereas a light-emitting module including an LED as the light-emitting device is called an LED module or the like.
In the conventional LD module or LED module, the optical fiber has a bare fiber section which is not covered with a covering (jacket), the bare fiber section extending from the light-receiving end to the neck portion. Due to this, light leakage occurs from the bare fiber section, which results in a local temperature increase inside the housing and/or in the vicinity of the neck portion. This makes it difficult to allow the LD or LED to operate at a predetermined temperature. As a conventional technique for addressing this problem, there has been a semiconductor laser module disclosed in Patent Literature 1.
The semiconductor laser module of Patent Literature 1 includes (i) a covering part covering cladding parts of a single mode fiber and (ii) an outer cladding part surrounding an inner cladding part, wherein each of the covering part and the outer cladding part is set to have a refractive index lower than that of the inner cladding part.
With this configuration, cladding-mode light guided through the cladding part of the single mode fiber is confined in the cladding part so as to be kept away from the housing. This prevents a local temperature increase inside the housing and/or in the vicinity of the neck portion.